Hi guys, I have a 1985 Corvette with a bunch of mods and stuff, my car is tuned but I still am using the 1985 ECM. When I rev the engine or accelerate, for a fraction of a second, my AFR gauge goes lean. Is this do to the ECM being slow and not being able to register the TPS and O2 sensor readings fast enough? Like is it normal? Thanks!

 

When you accelerate the ECM goes into open loop mode, so no O2 sensor.

Do you have software to look at the ECM tables and parameters? AE (Acceleration Enrichment) and PE (Power Enrichment) are where you should be looking.

 

Okay, I have a couple tables for Acceleration.

- "Accel. Enrich. Delta TPS Pulse Multiplier Vs. A.E. Pulse No."

- "Accel Enrich Delta TPS Pulse Multiplier Vs. Coolant Temp"

- "Accel Enrich Delta LV8 Factor Vs. Delta LV8"

- "Accel Enrich Delta LV8 Multiplier Vs. Coolant Temp"

- "Accel Enrich Delta LV8 Decay Rate Vs. Coolant Temp"

- "Delta TPS Accel Enrich Pulses Vs. Coolant Temp"

And one for Power Enrichment.

- "Power Enrichment Spark Vs. AFR"

Can you let me know which one of those tables I should be focusing on? I can post a picture of the data in my tables and maybe you can help me tweak them. Thanks!

 

I would suggest these tables and these constants.



- "Accel Enrich Delta TPS Pulse Multiplier Vs. Coolant Temp"

- "Accel Enrich Delta LV8 Factor Vs. Delta LV8"

- "Accel Enrich Delta LV8 Multiplier Vs. Coolant Temp"

- "Delta TPS Accel Enrich Pulses Vs. Coolant Temp

The 1985 ECM is touchy with acceleration tip in fuel going lean, you need to understand where the engine is going lean, is it light throttle tip in, heavy throttle tip in, is it temperature related and then adjust as necessary. You may also have to change when the car goes into power enrichment, by reducing the power enrichment throttle activation from 60% to maybe 25% to solve a lean tip in. Describe exactly what the problem is and I can narrow down your table choices.

 

Okay I can give you a list of all my problems, maybe you can help me.

The car runs really, really, really lean when it is cold. Let me explain from a cold start.

- If I leave it in the garage overnight and start it, it starts up fine.
- If it is left outside in the cold, doesn't even have to be overnight. It will be hard to start, sometimes stall. Today it stalled after it was hot and sat for about 20 minutes. I think it is open loop related.
- When it first starts, the idle is really low, between 450-600 RPMs.
- The AFR during a cold start is around 12:1, then it leans out to about 14.7:1 for a little bit, then goes really lean, 17:1, 18, 19, 20, 21, 22.4:1 Max AFR reading.
- As it gets warming, around 150 degrees, it starts to come down to around 14.7:1.
- When it hits closed loop, perfect, 14.7:1.
- When in open loop and revving, it bogs and backfires, the response takes about half a second for the engine to rev up after you press the pedal.
- When in closed loop, occasionally it will backfire when you rev it. I can see the AFR go to 22.4:1 for a fraction of a second when I rev it from an idle. If I'm at like 1500 RPMs or more and give it some more gas, it goes to maybe like 17:1 for a fraction of a second.
- When I drive it and come to a stop light, it surges between 550-750 RPMs, and then goes away, until I drive again and come to the next light.
- When it stops surging, it seems to idle at 600 - 650 ish RPMs. I would like it to idle at 725.

That's all the problems that I can think of. Tomorrow when I get to the shop, I will go through and see what different temperatures and light throttle tip in's to WOT tip in's and see what happens. Do you think you can help me solve most of those problems? Thank you so much!

 

Some of those symptoms sound like a bad CTS (Coolant Temperature Sensor) -- the one on the front of the intake manifold. It seems like the ECM thinks the engine is hot and acts accordingly.

It also sounds like you have a vacuum leak.

To verify some things that are implied by your post:

Are you still using the original ECM?
Do you have an external AFR gauge?
Stock O2 sensor or second one for the AFR gauge?
Do you have headers? (From "bunch of mods" I would guess yes.)
Do you have a heated O2 sensor?

 

The CTS sensor is new, but I mentioned in another thread that when my display reports 195 degrees, Tuner Pro RT says 160 degrees. Are you supposed to torque the CTS to specs for it to work properly? Because I only hand tightened it.

I've looked all over for a vacuum leak, I've sprayed starting fluid all around the intake, I've blocked off all the vacuum ports, I've use the cigar smoke trick, I've listened for it, can't find any.

- Yes, I'm using the original ECM.
- External AFR gauge meaning the one that I installed from innovate? Then yes, if that's not what you meant then no.
- I use a wideband for the AFR gauge, is it right behind the O2 sensor.
- Yes, I do have headers.
- Yes, I do have a heated O2 sensor.

If I send you my tune, can you look over it to see if everything is where is should be to confirm that it is not tune related? If not that's okay.

Thanks!

 

Okay, so here's what happened today. I started it, it was in the garage overnight, it's about 40 degrees farenheight inside. When I started it, it stalled. I started it again, it started surging and then evened out. The AFR was between 12-13. I revved it a little bit, on little dips of the throttle it gets really lean for half a second, like 20:1 AFR, and goes back down to around 12 - 13, finding it's way to 14 during the rev. I did some hard dips to the throttle and it went to 17:1 for half a second and went to around 12 - 13, and again finding it's way to 14. Had a few backfires, some out the intake, some out the exhaust.

After I stopped revving it, it settled down to 14.7:1 ish, but I noticed that the idle starts to drop from 700 down to 600 and the between 550-650. When it's at that point the AFR goes lean, like 17:1 or 18:1. If I rev it up again for a little bit and it sits at around 700, the AFR seems okay, until the idle drops again.

I didn't let it warm up all the way because I only needed to get it out of the garage so I could work on another car. Thanks for your help!

 

Your dash temp and ECM temp being off is normal, as I have the same ECM and I show the same thing (about 30 degrees higher on the dash). As for how your car is running, it doesn't sound like the tune is your problem to me....sounds like a vac leak. But you already checked for that.....

 

All of my experience is with the 1227165 ECM ('86 to '89). I don't know anything about the earlier ones (or later ones, for that matter). The only exception to that is that I have heard that the earlier ECMs are 160 baud only and the tuners don't like them because they don't get enough information from a data log.

I'm a hacker, not a tuner. There is a big difference. My car is totally stock, so I don't have any experience with tuner mods. My expertise is in understanding WHAT the ECM is doing and WHY it's doing it.